with John Maunder
A new model of the Sun’s interior is producing predictions of its behaviour with unprecedented accuracy; predictions with interesting consequences for Earth. Professor Valentina Zharkova of Northumbria University presented results for a new model of the Sun’s interior dynamo in a talk at the Astronomical Society meeting last week. (https://astronomynow.com/2015/07/09/royal-astronomical-societys-national-astronomy-meeting-2015-report-4/)
The Sun has an approximately 11-year activity cycle. During peak periods, it exhibits lots of solar flares and sunspots. Magnetic bubbles of charged particles (coronal mass ejections) may burst from the surface during this period, streaming material into space. These ejections can affect satellites and power lines on Earth. However, during lull periods, such activity may almost stop altogether. But the 11-year cycle isn’t quite able to predict all of the Sun’s behaviour — which can seem erratic at times. Zharkova and her colleagues (Professor Simon Shepherd of Bradford University, Dr Helen Popova of Lomonosov Moscow State University, and Dr Sergei Zarkhov of Hull University) have found a way to account for the discrepancies called a ‘double dynamo’ system.
The Sun, like all stars, is a large nuclear fusion reactor that generates powerful magnetic fields, similar to a dynamo. The model developed by Kharkov's team suggests there are two dynamos at work in the Sun; one close to the surface and one deep within the convection zone. They found this dual dynamo system could explain aspects of the solar cycle with much greater accuracy than before — possibly leading to enhanced predictions of future solar behaviour. “We found magnetic wave components appearing in pairs; originating in two different layers in the Sun’s interior. They both have a frequency of approximately 11 years, although this frequency is slightly different [for both] and they are offset in time,” says Zharkova. The two magnetic waves either reinforce one another to produce high activity or cancel out to create lull periods.
Comparison of three images over four years apart illustrates how the level of solar activity has risen from near minimum to near maximum in the Sun’s 11-years solar cycle. Image credit: SOHO/ESA/NASA.
Professor Zharkova and her colleagues used magnetic field observations from the Wilcox Solar Observatory in California for three solar cycles, from the period of 1976 to 2008. In addition, they compared their predictions to average sunspot numbers — another strong marker of solar activity. All the predictions and observations matched closely. Their predictions using the model suggest an interesting longer-term trend beyond the 11-year cycle.
It shows that solar activity is expected to fall by 60 % during the 2030’s, to conditions last seen during the ‘Maunder Minimum*’ of 1645-1715. “Over the cycle, the waves fluctuate between the Sun’s northern and southern hemispheres. Combining both waves together and comparing to real data for the current solar cycle, we found that our predictions showed an accuracy of 97 %,” says Zharkova.
The model predicts that the magnetic wave pairs will become increasingly offset during the Solar Cycle 25, which peaks in 2022. Then during Cycle 26, which covers the decade from 2030-2040, the two waves will become exactly out of synch, cancelling one another out. This will cause a significant reduction in solar activity. “In Cycle 26, the two waves exactly mirror each other, peaking at the same time but in opposite hemispheres of the Sun. We predict that this will lead to the properties of a ‘Maunder minimum’,” says Zharkova.
The sun was well observed during the period of the original “Maunder Minimum” and this lack of sunspots is well documented.This period of solar inactivity corresponded to a climatic period called the ‘Little Ice Age' when in Europe rivers that were normally ice-free, froze and snow fields remained at low altitudes throughout the year. There is evidence the sun had similar periods of inactivity during the years 1100-1250 and 1460-1550.
The connection between solar activity and the earth's climate is an area of ongoing and sometimes controversial research.Time will tell whether the sun will once again go into another “Maunder Minimum” within the lifetime of the present generation, and what affect it will have on our climate.
*The "Maunder Minimum" is the name given to the period from 1650 to 1700 when the number of sunspots became almost zero. The period is named after the solar astronomer Edward Walter Maunder (1851-1928) who while working at The Royal Observatory, Greenwich discovered the dearth of sunspots during the 1650-1700 period.
During one 30 year period within the Maunder Minimum there were only about 50 sunspots compared with a more typical 40,000. Maunder was a driving force in the foundation of the British Astronomical Association, and was a fellow of the Royal Astronomical Society.
For further information on a variety of weather and climate matters see: https://sites.google.com/images/theclimatedice/